Possible Timeline

Now that we have the offiical ages for the contestants in Ridonculous Race, we know that the original cast are all 19 years old now. This means Ridonculous Race takes place only 3 years after TDI, but where are the other seasons placed in between?

Here's what I think:

Total Drama Island was 8 weeks long, which is around 2 months, and obviously it took place during the Summer. So that means it possible took place between June and August 2007

Total Drama Action was 42 days long, and took place 2 days after TDI, so it was probably around mid-August to late September 2007.

Total Drama World Tour never had a specified amount of days, but we do know the finale was in early April, because of Cody's birthday, so I'd say TDWT took place around February to April 2008.

Total Drama: Revenge of the Island didn't give off any hints of when it took place, but judging by the length of Heather's hair, and the probability that it took place during the Summer again, I'd say it was just under 2 weeks long and took place in July 2008

Total Drama All-Stars took place a year after TDRI, and Alejandro also said he was in the Drama Machine for a year. If TDAS took place in around July 2009, then that could easilly mean Chris was in jail for exactly a year, and Alejandro was in the Drama Machine for a year and 3 months

Total Drama: Pahkitew Island was greenlit in-universe right at the end of TDAS, with Chris saying the producers wanted to go straight into a new season. This could mean TDPI took place in August 2009.

The Ridonculous Race is a little trickier, since it takes place around a time the original cast are all 19, but the TDPI cast are still 16. So that means it has to take place not too long before June, when TDI started in 2007. We know Cody turned 17 the following April, but it didn't look like anyone else had a birthday around then. I'd say RR takes place around May 2010.